A locked loop circuit operates to produce an output signal having a frequency that is a multiple, or fraction, of a reference frequency. In some cases, the reference frequency may be provided by a crystal oscillator. While a crystal oscillator accurately generate the reference frequency, it may be undesirably expensive, and may consume an undesirable amount of area.
Therefore, an RC oscillator may be used to generate the reference frequency for a locked loop circuit. However, due to process variations in fabrication of resistors and capacitors, an RC oscillator without a feedback mechanism may inaccurately generate such the reference frequency, which would result in the locked loop circuit employing that RC oscillator not actually generating its output signal as having a desired frequency.
Consequently, an RC oscillator used with a locked loop circuit will conventionally employ a feedback loop, calibration, or compensation circuit and be adjusted based thereupon. A digital to analog converter (DAC) is employed to generate control signals for components within the RC oscillator. By adjusting the operation of these components, the frequency of the signal generated by the RC oscillator may be adjusted.
Unfortunately, to obtain a high degree of accuracy in feedback signal generation with an RC oscillator, the DAC utilizes a large number of bits as input, resulting in the DAC being undesirably large and consuming an undesirable amount of area. In addition, a large DAC can consume an undesirable amount of power.
Therefore, further developments in the area of locked loop circuits is needed to address these issues.